The former US marine knew the calligraphy-covered flag he took from a fallen Japanese soldier 73 years ago was more than a keepsake of the second world war. When Marvin Strombo finally handed the flag back to Sadao Yasue’s younger brother and sisters on Tuesday, he understood what it really meant to them.

Younger brother Tatsuya Yasue buried his face into the flag and smelled it, then he held Strombo’s hands and kissed them. His elder sister Sayoko Furuta, sitting in her wheelchair, covered her face with both hands and wept silently as Tatsuya placed the flag on her lap.

As the first and only trace of their brother, the flag represented a treasure that would fill a deep void for Yasue’s family. Japanese authorities had only given them a wooden box containing a few rocks, a substitute for the remains that were never found.

It’s like the war has finally ended and my brother can come out of the limbo

Tatsuya Yasue

The flag’s white background is filled with the signatures of 180 friends and neighbours in the tea-growing mountain village of Higashishirakawa, wishing Yasue’s safe return.

“Good luck forever at the battlefield,” a message on it reads. Looking at the names and their handwriting, Tatsuya Yasue clearly recalls some of their faces and their friendship with his brother.

“The flag will be our treasure,” he said at his 400-year-old house. The 89-year-old farmer said the return of the flag brought closure. “It’s like the war has finally ended and my brother can come out of the limbo.”

Yasue last saw his older brother alive the day before he left for the South Pacific in 1943. The siblings had a small send-off picnic of sushi and Japanese sweet mochi for the oldest brother outside his military unit. It was their last meal together. At the end of the picnic, his brother lowered his voice, asking Tetsuya to take good care of their parents, as he was sent to fight in the Pacific islands, harsh battlegrounds where chances of survival were low.

A year later, the wooden box containing the stones arrived. Months after the war ended, the authorities told Yasue his brother died somewhere in the Marianas on July 18, 1944, at age 25.

“That’s all we were told about my brother, and we could only imagine what might have happened,” he said. Yasue and his relatives wondered if Sadao might have died at sea off Saipan. About 20 years ago, Yasue visited Saipan with his younger brother, imagining what their older brother might have gone through.

The only person who can provide some of those answers, Strombo, said he found Yasue’s body on the outskirts of Garapan when he got lost and ended up near the Japanese frontline. He told Yasue’s siblings that their brother is likely to have died of a concussion from a mortar round. He told them that Sadao was lying on his left, peacefully as if he was sleeping, not in pain.

At least the flag and his story suggested Yasue died on the ground, which raised hopes of retrieving his remains.

The remains of nearly half of 2.4 million Japanese war-dead overseas have yet to be found 72 years after the second world war ended. It’s a pressing issue as the bereaved families reach old age and memories fade.

Allied troops frequently took the flags from the bodies of their enemies as souvenirs. But to the Japanese bereaved families, they have a much deeper meaning, especially those like Yasue, who never learnt how their loved ones died and never received remains. The Japanese government has requested auction sites to stop trading wartime signed flags.

Strombo had the flag hung in a glass-fronted gun cabinet in his home in Montana for years, a topic of conversation for visitors. He was in the battles of Saipan, Tarawa and Tinian, which chipped away at Japan’s control of islands in the Pacific and paved the way for US victory.

In 2012, he was connected to an Oregon-based non-profit Obon Society that helps US veterans and their descendants return Japanese flags to the families of fallen soldiers. The group’s research traced it to the tea-growing village of 2,300 people in central Japan by analysing family names.